The ultimate aim of these studies is to develop potent antiestrogens capable of controlling growth of estrogen-dependent tumors in humans by non-invasive endocrine therapy. Because of their known specific interaction with estrogen receptors, antiestrogens seem particularly well suited to be specific, antitumor agents in the cases of estrogen-dependent tumors, theoretically capable of achieving non-surgical endocrine therapy. Our studies will assess the interaction of antiestrogens with estrogen receptors in target tissues and their in vivo pharmacokinetic behavior.